1. Field of the Invention
The present invention relates to an improved variable displacement swash plate type compressor suitable for use in a vehicle air conditioning system.
2. Description of the Related Art
FIG. 11 shows a conventional swash plate type of variable displacement compressor (hereinafter, simply referred to as a compressor). In this type of compressor, a rotary journal 103, which can tilt in the forward or backward direction along a drive shaft 100, is coupled, via a link pin 102, with a lug plate 101 mounted on the drive shaft 100. A swash plate 104 is coupled with the rotary journal 103. A plurality of cylinder bores 105 are provided in a cylinder block 110. Each one of the bores 105 accommodates a piston 106 that is connected to the swash plate 104 via a piston rod 107. The rotational motion of the rotary journal 103 causes undulating movement of the swash plate 104, which in turn drives the connecting rods and pistons one after another in a linear reciprocating manner.
An elongated hole 109 is formed in a support arm 108 which protrudes from the lug plate 101. The link pin 102 is slidably fitted into the elongated hole 109. Therefore, this fitting design permits the tilting motions of the journal 103 and the swash plate 104. When the piston 106 is at the end of the compression stroke, the top clearance of the piston 106 within the corresponding bore 105 is approximately kept constant. Therefore, the top position of the swash plate 104 does not cause to displace in the front-and-rear direction, regardless of the change of the inclination angle of the swash plate 104. The top clearance is defined as a gap between a valve plate 111 which closes the opening of the bore 105, and the head portion of the piston 106 which is at the end of the compression stroke. Further, the top position of the swash plate 104 is defined as the point where the swash plate 104 is at the closest to the bore 105, according to the undulating movement of the swash plate 104. A sleeve 112 is slidably attached to the drive shaft 100. The rotary journal 103 is pivotally supported by a sleeve pin 113, on the sleeve 112.
In the conventional compressor, when the dimensional accuracy of the elongated hole 109 which guides the pin 102 is low, the top clearance of the piston 106 is difficult to maintain at the approximately constant level, regardless of the change of the tilt angle of the swash plate 104. When the gap between the elongated hole 109 and the pin 102 is rather great, noise is generated therefrom. It is difficult to further improve the dimensional accuracy of the elongated hole 109.
However, the conventional compressor described above is designed such a way that a point of application (Mf) of the compression reaction force which is exerted on the swash plate 104 via the corresponding piston 106 and piston rod 107, and a point of support (Mk) of the compression reaction force via the pin 102 within the elongated hole 109, will be arranged on the line in parallel to the axis of the drive shaft, when the discharge capacity of the compressor is at the maximum, as the inclination angle of the swash plate 104 is at the maximum. Therefore, as the inclination angle of the swash plate decreases, the point of support (Mk) of the compression reaction force via the pin 102 is downwardly moved along the elongated hole 109. Further, the point of application (Mf) arranged on the swash plate 104 which receives the compression reaction force generated by the piston 106 at the top position, is relatively moved upward, with respect to the point of support (Mk).
As a result, the point of application (Mf) of the compression reaction force via the piston 106 at the top position recedes away from the drive shaft 100, further than the point of support (Mk) of the compression reaction force via the pin 102. Therefore, the moment, which causes the inclination angle of the swash plate 104 to further decrease based on the compression reaction force, is generated. The movement of the swash plate 104 toward the decreasing side of the discharge capacity becomes sensitive, based on the influence of this moment. Contrary, the movement of increasing the inclination angle of the swash plate 104 is considerably obstructed by the moment. Therefore, the movement of the swash plate 104 toward the increasing side of the discharge capacity becomes unresponsive. Thus, the overall control for the discharge capacity is not always satisfactory.